The goal of this proposed grant is to advance the understanding of the mechanisms of action by which the human innate and acquired immune systems protect from Entamoeba histolytica disease. Humans vary in their susceptibility to disease, and 90% of those who acquire E. histolytica infection remain asymptomatic. While there are many host, pathogen, and environmental factors that influence disease development, undoubtedly the host's immune response, as determined by their genetic make up, plays a primary role. The proposed research will address two major aims. Aim 1 will study gene expression at the mRNA and protein level by determining cytokine responses associated with resistance or susceptibility to E. histolytica disease. The study cohort will involve children already being prospectively observed for diarrheal disease in Dhaka, Bangladesh, an area endemic for E. histolytica infection. We intend to use cultured PBMCs to determine cytokine responses from both the innate and acquired immune responses. We will measure cytokines at baseline (while uninfected) in children who have never had E. histolytica infection, children who have had asymptomatic colonization only, and children who have had invasive disease. We will also measure cytokines in children who have current asymptomatic E. histolytica infection and children with active E. histolytica diarrhea. In addition, fecal cytokines will be measured during colonization vs. diarrheal disease from E. histolytica to sample more specifically the mucosal immune response. Aim 2 will genotype a cohort of children in order to determine associations between single nucleotide polymorphisms (SNPS) in immune response genes and resistance or susceptibility to E. histolytica disease. The genes studied in Aim 1 will be genotyped in Aim 2, therefore significant SNPS can be evaluated for associations with cytokine gene function. Amebiasis, primarily due to Entamoeba histolytica, remains an important cause of morbidity and mortality in the developing world. Successful completion of these studies will allow us to determine the functional consequences of genetic polymorphisms in cytokine genes, and their association with E. histolytica infection and disease. This will provide insight into the mechanisms by which the human immune system protects against amebiasis.